fix(ai): seq2seq models causing null pointer error

- Solved the "`GetMutableData` should not be a null pointer" error while
executing seq2seq models.
- Ref.: pykeio/ort#185

crates/sb_ai/onnxruntime/tensor.rs

@@ -15,36 +15,46 @@ use serde::{Deserialize, Serialize};
 // but it only allows [u8] instead of [T], so we need to get into `unsafe` path.
 macro_rules! v8_slice_from {
     (tensor::<$type:ident>($tensor:expr)) => {{
-        let (_, raw_tensor) = $tensor
-            .try_extract_raw_tensor_mut::<$type>()
-            .map_err(AnyError::from)?;
-
-        let tensor_ptr = raw_tensor.as_ptr();
-        let tensor_len = raw_tensor.len();
-        let tensor_rc = Rc::into_raw(Rc::new(raw_tensor)) as *const c_void;
+        // We must ensure there's some detection to avoid `null pointer` errors
+        // https://github.com/pykeio/ort/issues/185
+        let n_detections = $tensor.shape()?[0];
+        if n_detections == 0 {
+            let buf_store = v8::ArrayBuffer::new_backing_store_from_vec(vec![]).make_shared();
+            let buffer_slice =
+                unsafe { deno_core::serde_v8::V8Slice::<u8>::from_parts(buf_store, 0..0) };
+
+            buffer_slice
+        } else {
+            let (_, raw_tensor) = $tensor
+                .try_extract_raw_tensor_mut::<$type>()
+                .map_err(AnyError::from)?;
+
+            let tensor_ptr = raw_tensor.as_ptr();
+            let tensor_len = raw_tensor.len();
+            let tensor_rc = Rc::into_raw(Rc::new(raw_tensor)) as *const c_void;
+
+            let buffer_len = tensor_len * size_of::<$type>();
+
+            extern "C" fn drop_tensor(_ptr: *mut c_void, _len: usize, data: *mut c_void) {
+                // SAFETY: We know that data is a raw Rc from above
+                unsafe { drop(Rc::from_raw(data.cast::<$type>())) }
+            }
 
-        let buffer_len = tensor_len * size_of::<$type>();
+            let buf_store = unsafe {
+                v8::ArrayBuffer::new_backing_store_from_ptr(
+                    tensor_ptr as _,
+                    buffer_len,
+                    drop_tensor,
+                    tensor_rc as _,
+                )
+            }
+            .make_shared();
 
-        extern "C" fn drop_tensor(_ptr: *mut c_void, _len: usize, data: *mut c_void) {
-            // SAFETY: We know that data is a raw Rc from above
-            unsafe { drop(Rc::from_raw(data.cast::<$type>())) }
-        }
+            let buffer_slice =
+                unsafe { deno_core::serde_v8::V8Slice::<u8>::from_parts(buf_store, 0..buffer_len) };
 
-        // Zero-Copying using ptr
-        let buf_store = unsafe {
-            v8::ArrayBuffer::new_backing_store_from_ptr(
-                tensor_ptr as _,
-                buffer_len,
-                drop_tensor,
-                tensor_rc as _,
-            )
+            buffer_slice
         }
-        .make_shared();
-
-        let buffer_slice =
-            unsafe { deno_core::serde_v8::V8Slice::<u8>::from_parts(buf_store, 0..buffer_len) };
-
-        buffer_slice
     }};
 }
 
@@ -152,7 +162,7 @@ pub struct ToJsTensor {
     #[serde(rename = "type", with = "JsTensorType")]
     data_type: TensorElementType,
     data: ToJsBuffer,
-    dims: Vec<i64>,
+    pub dims: Vec<i64>,
 }
 
 impl ToJsTensor {